Current sense amplifiers are used in a wide variety of applications, including automotive, power supply, computing, medical, telecommunications, industrial and wireless applications. A current sense amplifier monitors the current flowing through a load within a circuit. Monitoring may be classified as low side sensing, where the sense amplifier detects the voltage across a resistor coupled between the load and ground, or as high side sensing, where the sense amplifier detects the voltage across a resistor coupled between the supply rail and the load.
One design constraint that affects sense amplifiers used in high side sensing is the maximum allowable common mode (CM) voltage present at the input of the amplifiers (i.e., a voltage of equal magnitude applied to both amplifier inputs resulting in a differential input voltage of zero). This is because high side sensing configurations can expose the amplifier inputs to much higher common mode voltages than those typically present in low side configurations, which can damage or destroy the amplifier's input devices if the applied voltage exceeds their limits. Designing and manufacturing a sense amplifier that is accurate and sensitive with a low referred to input (RTI) offset voltage (i.e., the output offset voltage divided by the amplifier's closed-loop gain) and a high common mode rejection ratio (CMRR), equal to the ratio of the differential gain to the absolute value of the common mode gain, yet that is still capable of being subjected to high CM input voltages (including transient spikes) above the supply rail, can be challenging.
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